(1) Field of the Invention
The present invention relates to an alignment measurement apparatus and a method for using the same for use during an exposure process for forming a phosphor screen in a color cathode-ray tube, and more particularly to an alignment measurement apparatus and a method for using the same with which it is possible to make a precise measurement of an exposure pattern of 3-color phosphor dots.
(2) Description of the Related Art
Generally, in a color cathode-ray tube of a shadow mask type, a black matrix film composed of a light absorbing material layer is formed on an inside surface of a panel facing a shadow mask disposed inside the panel, and fine dot-like phosphor layers which respectively emit red, green and blue colors are formed at opening portions of the black matrix film. The phosphor layers are generally formed sequentially for one color at a time by a precision photo exposure method utilizing a photosensitive material. During the formation of each of the phosphor layers, it is required to make an advance correction of the location of the panel by measuring in advance the degree of any deviation between the exposure patterns and the black matrix holes caused by an exposure apparatus, and this makes it necessary to use an alignment measurement apparatus.
Conventionally, the alignment measurement has been carried out by using an exposure apparatus as shown in FIG. 1. The exposure apparatus is constituted by a table 2 which is finely adjustable and which carries and positions reference panel 1, a light source 3 disposed under the table 2, and a correcting lens 4 and a light adjusting filter 5 disposed between the table 2 and the light source 3. The table 2 carries the test reference panel 1 coated with a green phosphor having good emission properties with respect to ultraviolet rays from a mercury lamp as the light source 3 for the exposure, whereby the exposure patterns at a peripheral portion of an outside surface of the reference panel 1 are photographed with magnification by a CCD camera 6, the black matrix holes and the exposure pattern images are observed by a picture image monitor 8, the reference panel 1 is moved three dimensionally by the table 2, and the center of each black matrix holes and the center of the emitted light of each exposure pattern are brought into coincidence with each other. From the degree of this movement, the degree of deviation is measured and the alignment measurement is carried out.
Normally, as an apparatus for measuring black matrix holes of a color cathode-ray tube of the above kind, it is arranged such that, for purposes of eliminating a measurement error caused by external light 9, an external light shielding plate 7 is provided to cover a periphery of the light receiving surface of a measuring sensor (CCD camera 6 in FIG. 1) as disclosed, for example, in Japanese Utility Model Kokai Publication No. Hei 1-165410.
However, since the excitation emission of phosphor by the ultraviolet light, as used for a light source for the exposure, is very weak, and the light transmitted through the phosphor layer is small and is scattered, the image of the exposure pattern is of low luminosity and is blurred as shown in FIG. 2. Thus, where the external light shielding plate as described above covers a portion of the light receiving surface to make the measuring environment dark, the black matrix holes cannot be observed clearly, so that the alignment measurement precision may be at a maximum on the order of 10 .mu.m. However, recently, a high precision color cathode tube has been manufactured with the diameter of the black matrix hole reduced to smaller than 90 .mu.m, which requires the measuring precision to be within 2 .mu.m but this requirement has not been met in the past.
A further problem in the above prior art example is that, since the alignment measurement is done visually and manually, it takes a long time for the measuring operation.